Abstract
We developed a novel rapid analysis method to measure trace levels of radiocaesium in surface water by using absorbent disks for radioactive caesium with a NaI scintillation counter (ADiCS). ADiCS involves 1) the selective absorption of dissolved radiocaesium onto the disk and the collection of particulate radiocaesium on the PTFE membranes by surface water filtration and then 2) directly measuring the radioactivity on PTFE membranes and the disk by a NaI scintillation counter. Evaluation of the accuracy and rapidity of ADiCS for 20 L samples with less than 20 mg•L-1 suspended solids showed that ADiCS needed six times less concentration time than the evaporation method and that the limit of detection was approximately 10 mBq•L-1. Moreover, radioactivity data obtained by ADiCS had less than 30 % of the error of data obtained by the evaporation method. ADiCS also revealed a significant increase in radiocaesium in the Kanto region after the nuclear power plant accident. Especially, a radiocaesium concentration of over 100 mBq•L-1 was observed in surface water around high radiocaesium deposition areas. These results indicated ADiCS can evaluate current and future trace levels of radiocaesium in surface water, including bioaccumulation characteristics, more easily than the evaporation method.
